**Core Concept**
The Revised National Tuberculosis Control Programme (RNTCP) in India relies on a case-finding approach to identify and treat tuberculosis (TB) patients. This approach is based on the principles of active case-finding, which involves screening high-risk populations to detect TB cases earlier.

**Why the Correct Answer is Right**
The RNTCP uses a combination of passive and active case-finding methods. Passive case-finding relies on patients seeking medical attention and reporting their symptoms to healthcare providers. In contrast, active case-finding involves proactive screening of high-risk populations, such as those living in close proximity to known TB cases, individuals with HIV/AIDS, and people who have recently traveled to high-prevalence areas. The RNTCP's active case-finding strategy involves screening these populations through sputum smear microscopy and chest radiography.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because passive case-finding alone is not sufficient to control TB, as it relies on patients seeking medical attention, which may be delayed.
**Option B:** This option is incorrect because while symptom-based screening is a component of active case-finding, it is not the sole basis of the RNTCP's case-finding strategy.
**Option C:** This option is incorrect because while contact tracing is an important component of TB control, it is not the primary basis of the RNTCP's case-finding approach.

**Clinical Pearl / High-Yield Fact**
The RNTCP's active case-finding strategy has been instrumental in reducing the incidence of TB in India, with a significant increase in the number of detected cases and a corresponding decrease in mortality rates.

**Correct Answer: C. Contact tracing.**